Electronic signals are acted upon by transmission through various systems, conduits or the like. These conduits have various inherent physical properties, one of them being impedance. This impedance is the total opposition to the flow of current offered by a circuit. A transmission line that is terminated with a load impedance equal to the characteristic impedance Zo of the line will not reflect an incident wave at that point, and the transmission line is said to be impedance matched. However, a transmission line that is terminated with a load impedance different than Zo will reflect part of an incident wave back toward the source or generator of the signal.
Reflections are often undesirable and should be eliminated. This is because at any point along the transmission line, that value of the signal will appear as a combination of the originally transmitted signal, and the reflected signal, thus resulting in distortion of the originally transmitted signal. Indeed, the voltage seen at any particular point on the line will be the vector sum of the transmitted and reflected sinusoids. Because the phase between the transmitted and reflected signals varies with position along the signal line, the vector sums at different points along the transmission paths will be different, thus affecting the actual signal present on the transmission line, and at the output thereof.